Color liquid crystal display

ABSTRACT

In a reflection-type color liquid crystal display which can display a bright, high-saturation negative-type color display with a background in black or deep color, a pair of polarizing films  8  and  9  are disposed on both sides of a liquid crystal  20  which has a nematic liquid crystal  7  between a pair of substrates  1  and  4  having electrodes respectively, and a twisted retardation film  10  is disposed between the polarizing films  9  and the liquid crystal device  20.  The intersecting angle between absorption axes of the pair of polarizing films  8  and  9  is set to be in the range of 60° to 120°, the Δnd value of the liquid crystal device  20  is set to be in the range of 1500 nm to 1800 nm, and the Δnd value of the twisted retardation film  10  is arranged to be in nearly the same range as the Δnd value of the liquid crystal device  20.

This application is a division or prior application Ser. No. 09/096,492filed Jun. 12, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a color liquid crystal display, moreparticularly, to a color liquid crystal display performing color displayusing birefringence of a liquid crystal device, without using colorfilters.

2. Description of the Related Art

There are two kinds of color liquid crystal displays, that is, oneembodies a color filter and the other performs color display usingbirefringence of a liquid crystal without using a color filter.

In a liquid crystal display having a color filter therein, since a pixelis composed of three elements of R, G, B, the amount of transmittedlight is reduced to around one third and the liquid crystal displayusually requires a small fluorescent light as a back light, the liquidcrystal display with a color filter is not suitable for areflection-type color liquid crystal display.

On the other hand, a liquid crystal display which performs color displayutilizing birefringence of a liquid crystal is suitable for thereflection-type color liquid crystal display, because color displayingcan be performed with one pixel only by changing the voltage applied toa liquid crystal device.

As the color display utilizing the birefringence of the liquid crystal,the followings are known:

(1) A color liquid crystal display composed only of a liquid crystaldevice and a pair of polarizing films.

(2) A color liquid crystal display composed of a liquid crystal device,a retardation film and a pair of polarizing films.

(3) A color liquid crystal display composed of a liquid crystal device,a twisted retardation film and a pair of polarizing films.

As a liquid crystal device for a color liquid crystal display, ahomogeneous liquid crystal device having a twisted angle of zerodegrees, a TN (twisted nematic) liquid crystal device having a twistedangle of 90 degrees, and an STN (super twisted nematic) liquid crystaldevice having a twisted angle between 180 to 270 degrees have beendeveloped.

A conventional example of a color liquid crystal display using a twistedretardation film and adopting an STN liquid crystal device as a liquidcrystal device will be explained with reference to FIG. 16 to FIG. 18.

FIG. 18 is a schematic sectional view of the above-described colorliquid crystal display, FIG. 16 is a plan view showing a relationbetween the absorption axes of lower polarizing films and the molecularalignment direction in the liquid crystal, obtained when FIG. 18 isviewed from the upper polarizing film 9 side, and FIG. 17 is also a planview showing a relation between the absorption axes of the upperpolarizing film and the twisted retardation film.

Such a color liquid crystal display is disclosed, for instance, inJapanese Patent Laid-open No. Hei 7-5457.

In the color liquid crystal display, as shown in FIG. 18, a liquidcrystal device 20 is formed by holding a nematic liquid crystal 7 in atwisted alignment between a pair of substrates composed of a firstsubstrate 1 which is formed with an alignment layer 3 and a firstelectrode 2 made of ITO (Indium Tin Oxide) and a second substrate 4which is formed with an alignment layer 6 and a second electrode 5 madeof ITO.

Further, a pair of polarizing films, that is, a lower polarizing film 8and an upper polarizing film 9, are disposed holding the above-describedliquid crystal device 20 thereinbetween, a twisted retardation film 10is disposed between the liquid crystal device 20 and the upperpolarizing film 9, and a reflecting plate 11 is disposed outside of thelower polarizing film 8.

Absorption axes (or transmission axes) of the pair of polarizing films 8and 9 are disposed in parallel. Here, the twisted angle of the liquidcrystal device 20 is 250 degrees. The absorption axis 8 a of the lowerpolarizing film 8 shown by a broken line with arrows in FIG. 16intersects with the lower molecular alignment direction 7 a in theliquid crystal, that is the alignment direction of the liquid crystal inthe first substrate 1, at an angle of 45 degrees. The absorption axis 9a of the upper polarizing film 9 shown by a solid line with arrows inFIG. 17 is disposed to intersect with the upper molecular alignmentdirection 10 b in the twisted retardation film 10 at an angle of 45degrees.

Incidentally, the reference numeral 7 b in FIG. 16 shows the uppermolecular alignment direction in the liquid crystal, that is thealignment direction in the liquid crystal of the second substrate 4, andthe reference numeral 10 a in FIG. 17 shows the lower molecularalignment direction in the twisted retardation film 10.

The Δnd value of the liquid crystal device 20 expressed by the productof a difference of the birefringence Δn of the nematic liquid crystal 7and a cell gap d, that is a space between the first substrate 1 and thesecond substrate 2, is 843 nm. A twisted angle of the twistedretardation film 10 is 250 degrees in the reverse direction of thetwisted angle of the liquid crystal device 20. The Δnd value of thetwisted retardation film, which is expressed by the product of adifference Δn of the birefringence of the twisted retardation film 10and the thickness d, is also 843 nm.

As shown in FIG. 17, since the absorption axis 9 a of the upperpolarizing film 9 is disposed to intersect with the upper molecularalignment direction 10 b in the twisted retardation film 10 at an angleof 45 degrees, linearly polarized light incident from the upperpolarizing film 9 becomes elliptic polarized after passing through thetwisted retardation film 10.

However, since the upper molecular alignment direction 7 b of the liquidcrystal in the liquid crystal device 20 deviates from the lowermolecular alignment direction 10 a in the twisted retardation film by 90degrees, the elliptic polarized light generated at the liquid crystaldevice 20 and the twisted retardation film 10 is placed back into itsoriginal state of linearly polarized light and reaches the lowerpolarizing film 8. Since the absorption axis 8 a of the lower polarizingfilm 8 is parallel to the absorption axis 9 a of the upper polarizingfilm 9, a white display is shown.

When voltage is applied between the first electrode 2 and the secondelectrode 5, the liquid crystal molecules 7 are activated and theapparent Δnd value of the liquid crystal device 20 is decreased.Accordingly, the elliptic polarized light generated at the twistedretardation film 10 cannot be completely canceled by the liquid crystaldevice 20, and reaches the lower polarizing film 8 without changing itselliptical polarization state. Accordingly, light beams having aspecific wavelength penetrate therethrough and generate several colors.

The light that has passed through the lower polarizing film 8 isreflected by a reflecting plate 11 and emits upwards again after passingthrough the lower polarizing film 8, the liquid crystal device 20, thetwisted retardation film 10 and the upper polarizing film 9. Thus, areflection-type color display can be obtained. That is, it can displayin white when no voltage is applied, but according to a voltageincrease, it can display in several colors such as yellow, violet, redand so on.

Next, a conventional color liquid crystal display using a retardationfilm and adopting an STN liquid crystal device as a liquid crystaldevice will be explained with reference to FIG. 19 to FIG. 21. FIG. 21is a schematic sectional view of the color liquid crystal display, FIG.19 is a plan view showing a relation between absorption axes of a lowerpolarizing film and the molecular alignment direction in the liquidcrystal obtained when FIG. 21 is viewed from the upper polarizing film 9side, and FIG. 20 is also a plan view showing a relation betweenabsorption axes of an upper polarizing film and the phase delay axis ofeach retardation film.

Such a color liquid crystal display is disclosed, for instance, inJapanese Patent Laid-open No. Hei 8-15691.

As shown in FIG. 21 the color liquid crystal display is comprised of: aliquid crystal device 21 (the twisted angle is the same as that of theliquid crystal device 20 in FIG. 18 but the cell gap is different); apair of polarizing films, that is, a lower polarizing film 8 and anupper polarizing film 9, disposed holding the liquid crystal device 21thereinbetween; a first retardation film 15 and a second retardationfilm 16 disposed between the liquid crystal device 21 and the upperpolarizing film 9; and a reflecting plate 11 disposed outside of thelower polarizing film 8.

The absorption axes (or transmission axis) of the pair of polarizingfilms 8 and 9 are disposed intersecting at almost right angles. Here,the twisted angle of the liquid crystal device 21 is 250 degrees. Theabsorption axis 8 a of the lower polarizing film 8 shown by a brokenline with arrows in FIG. 19 intersects with the lower molecularalignment direction 7 a in the liquid crystal, that is an alignmentdirection of the liquid crystal in the first substrate 1, at an angle of45 degrees. The phase delay axis 16 a of the second retardation film 16shown by a broken line in FIG. 20 is disposed to intersect with theupper molecular alignment direction 7 b of the liquid crystal in theliquid crystal device 21 at an angle of 95 degrees, and the absorptionaxis 9 a of the upper polarizing film 9 shown by a solid line witharrows in FIG. 20 is disposed to intersect with the phase delay axis 15a of the first retardation film 15 at an angle of 15 degrees.

The Δnd value of the above described liquid crystal device 21 is between1530 nm and 1730 nm. The retardation value of the first retardation film15 is 1600 nm and the retardation value of the second retardation film16 is 1550 nm.

Since the absorption axis 9 a of the upper polarizing film 9 and thephase delay axis 15 a of the first retardation film 15 intersect witheach other at an angle of 15 degrees, linearly polarized light incidentfrom the upper polarizing film 9 becomes elliptic polarized afterpassing through the first retardation film 15 and the second retardationfilm 16.

However, since the upper molecular alignment direction 7 b of the liquidcrystal in the liquid crystal device 21 and the phase delay axis 16 a ofthe second retardation film 16 deviate from each other by about 90degrees, elliptic polarized light generated at the first retardationfilm 15 and the second retardation film 16 is returned to almost itsoriginal state as linearly polarized light to reach the lower polarizingfilm 8. Since the absorption axis 8 a of the lower polarizing film 8intersects with the absorption axis 9 a of the upper polarizing film 9at almost right angles, a black state is obtained.

When voltage is applied to the first electrode 2 and the secondelectrode 5, the molecules of the nematic liquid crystal 7 are activatedand the apparent Δnd value of the liquid crystal is decreased.Accordingly, since the elliptic polarized state generated at the firstretardation film 15 and the second retardation film 16 cannot becompletely canceled by the liquid crystal 21 and reaches the lowerpolarizing film 8 without changing its elliptic polarized state, lightbeams having specific wavelengths transmit and generate a plurality ofcolors.

Since the beams passing through the lower polarizing film 8 arereflected by the reflecting plate 11, and again pass through the lowerpolarizing film 8, the liquid crystal device 21, the second retardationfilm 16, the first retardation film 15, and the upper polarizing film 9,and then emit upward, a reflection-type color display can be obtained.That is, it displays in black when no voltage is applied, but accordingto voltage increase, it displays in several colors such as white, red,blue, green and the like.

However, in an actual color liquid crystal display, since variations inevery wavelength dependence of Δn in the birefringence of the liquidcrystal material are different from the variations in every wavelengthdependence of Δn in birefringence of the retardation film or the twistedretardation film, good background colors or tints cannot be obtainedwith a conventional arrangement of the polarizing films as describedabove.

With regard to a negative-type display for changing colors of letterswhile displaying the background color in black, the above describedliterature discloses that it is possible to dispose the absorption axis9 a (or transmission axis) of the upper polarizing film 9 and theabsorption axis 8 a (or transmission axis) of the lower polarizing film8 in a manner that they intersect with each other at almost rightangles. However, the literature does not disclose the best conditionsuitable for coloring the negative-type display, and a reflection-typecolor liquid crystal display which makes display possible in bright andgood color saturation has not yet become practical.

SUMMARY OF THE INVENTION

The present invention is conducted in consideration the presentsituation and the object of the present invention is to provide areflection-type color liquid crystal display for a negative-type displayto display colored letters and patterns in bright and good colorsaturation while the background color is displayed in black or in a deepcolor by optimizing a disposition angle between a liquid crystal deviceand a sheet of retardation films or a twisted retardation films and apolarizing film, or the like.

In order to achieve the above-described object, in a color liquidcrystal display comprising a liquid crystal device holding a nematicliquid crystal in a twisted alignment between a pair of substratescomposed of a first substrate having a first electrode and a secondsubstrate having a second electrode, a pair of polarizing films holdingthe liquid crystal device thereinbetween, and a twisted retardation filmdisposed between the liquid crystal device and one of the pair ofpolarizing films, the present invention is characterized in thefollowing configuration.

That is, an angle formed between absorption axes of the pair ofpolarizing films is set to be in a range between 60 degrees and 120degrees, a Δnd value of the above-described liquid crystal device is setin a range between 1500 nm and 1800 nm, and the Δnd value of the abovetwisted retardation film is set to be in nearly the same range as theΔnd value of the liquid crystal device.

As aforementioned, the Δnd value of the liquid crystal device isexpressed by the product of a difference Δn of the birefringence of thenematic liquid crystal and a cell gap d, that is a space between thefirst substrate and the second substate, and a Δnd value of the twistedretardation film is expressed by the product of a difference Δn of thebirefringence of the twisted retardation film and the thickness d.

Instead of or in addition to the Δnd value of both the above-describedliquid crystal device and the Δnd value of the twisted retardation filmbeing made to be in the range of 1500 nm to 1800 nm, the twist directionof the twisted retardation film may be set to be in the reversedirection with respect to a twist direction of the liquid crystaldevice, and the absolute value of the twisted angle of the twistedretardation film may be made larger than the absolute value of thetwisted angle of the liquid crystal device by an angle of 5 to 30degrees.

It is preferable to provide a reflecting plate outside of the polarizingfilm disposed on the opposite side of the twisted retardation film forthe above-described color liquid crystal display.

One or both of the pair of polarizing films may be a colored polarizingfilm prepared by dying with dyestuffs.

The above-described twisted retardation film may be atemperature-compensating type twisted retardation film in which a Δndvalue of the twisted retardation film varies in accordance withtemperature.

In a color liquid crystal display comprising a liquid crystal deviceholding a nematic liquid crystal in a twisted alignment between a pairof substrates composed of a first substrate having a first electrode anda second substrate having a second electrode, a pair of polarizing filmsholding the liquid crystal device thereinbetween, and a retardation filmdisposed between the liquid crystal device and one of the pair ofpolarizing films, the present invention may be structured in thefollowing manner.

An intersecting angle formed between the absorption axis of a polarizingfilm disposed at the opposite side of the above-mentioned retardationfilm in relation to the above described liquid crystal device and thelower molecular alignment direction of the liquid crystal in the liquidcrystal device is set to be in the range of 35±10 degrees, a Δnd valueof the above-described liquid crystal device is set to be in the rangebetween 1500 nm and 1800 nm, and the retardation value of theabove-described retardation film is set to be larger than a Δnd value ofthe above-described liquid crystal device by 50 nm to 200 nm.

Alternatively, a Δnd value of the above-described liquid crystal devicemay be taken in the range of 1300 nm to 1600 nm, and the retardationvalue of the above-described retardation film may be taken to be largerthan a Δnd value of the above-described liquid crystal device by 300 to500 nm.

In the above-described color liquid crystal display, as theabove-described retardation film, a biaxial retardation film, in whichthe relation among the refractive index nx of the phase delay axis ofthe retardation film, the refractive index ny in the y axis direction,and the refractive index nz in the z axis direction is: nx>nz>ny, may beused.

A reflecting plate may be provided outside of the polarizing filmdisposed at the opposite side of the retardation film in relation to theliquid crystal device.

Alternatively, one or both of the above-described pair of polarizingfilms may be a colored polarizing film prepared by dying with dyestuffs.

The above-described retardation film may be replaced with atemperature-compensating type retardation film of which the retardationvalue varies in accordance with temperature.

In the color liquid crystal display according to the present invention,linearly polarized light incident from the upper polarizing film 9penetrates into the twisted retardation film to become ellipticallypolarizing light. When no voltage is applied, a Δnd value of the liquidcrystal device and a Δnd value of the twisted retardation film arenearly the same. Therefore the elliptic polarized light is returned to alinearly polarized state by the liquid crystal device. The absorptionaxes of a pair of polarizing films composed of the lower polarizing filmand the upper polarizing film form an angle of 60 to 120 degrees.Linearly polarized light emitted through the liquid crystal device isblocked by the lower polarizing film to produce display in black.

In another color liquid crystal display according to the presentinvention, after linearly polarized light incident from an upperpolarizing film enters into a retardation film, since an absorption axisof the upper polarizing film and a phase delay axis of the retardationfilm form an angle of 45 degrees, the linearly polarized light becomeselliptic polarized light. Since the upper molecular alignment directionin the liquid crystal device and the phase delay axis of the retardationfilm form an angle of 85 degrees, that is almost orthogonal, the liquidcrystal device acts to cancel the elliptic polarized light generatedfrom the retardation film.

However since the liquid crystal device twists itself, in order tocompletely cancel the elliptical polarization state generated from theretardation film, a Δnd value of the liquid crystal device and aretardation value of the retardation film are designed to have adifference, and the absorption axis of the lower polarizing film and thelower molecular alignment direction in the liquid crystal are arrangedto intersect at an angle of 35 degrees, so that the polarized lightcompletely returns to the linearly polarized state to display in blackwhen no voltage is applied.

In any case, when voltage is applied between a first electrode and asecond electrode of a liquid crystal device, an apparent Δnd value ofthe liquid crystal device decreases, elliptic polarized light generatedfrom a twisted retardation film or retardation film does not completelyreturn back to linearly polarized light, and only beams having a certainwavelength can pass through the lower polarizing film, allowing a colordisplay.

By arranging the absorption axis of the upper polarizing film and theupper molecular alignment direction in the twisted retardation film toform an angle in the range from 35 to 40 degrees or from 50 to 55degrees, compensation for degradation of blackness on the backgroundgenerated from a difference between the wavelength dependency of adifference Δn of birefringence of the twisted retardation film 10 andthe wavelength dependence of a difference of birefringence Δn ofbirefringence of the liquid crystal, and degradation of color saturationof the display can be performed better than in the case where an anglebetween the absorption axis of the upper polarizing film and the uppermolecular alignment direction in the twisted retardation film is set tobe 45 degrees.

Similarly, by arranging the absorption axis of the lower polarizing filmand the lower molecular alignment direction of the liquid crystal in theliquid crystal device to form an angle in the range from 35 to 40degrees or from 50 to 55 degrees, compensation for degradation ofblackness on the background generated from a difference betweenwavelength dependency of a difference Δn of birefringence of the twistedretardation film 10 and the wavelength dependency of a difference Δn ofbirefringence of the liquid crystal, and degradation of color saturationof the display can be performed better than in the case where the anglebetween the absorption axis of the lower polarizing film and the lowermolecular alignment direction of the liquid crystal in the liquidcrystal is taken to be 45 degrees.

Further, in each case, by arranging a Δnd value of the liquid crystaldevice and a Δnd value of the twisted retardation film in a range from1500 nm to 1800 nm, an apparent Δnd value largely varies with a slightdifference in applied voltage, so that it becomes possible to change thecolor from black to a final color of green, which makes it possible todisplay in several colors even with a high multiplex drive.

When a twisted retardation film is used, by arranging the twistdirection of the twisted retardation film in the reverse direction tothe twist direction of the liquid crystal device, and by making theabsolute value of the twisted angle of the twisted retardation filmlarger than the absolute value of the twisted angle of the liquidcrystal device, the wavelength dependency of the difference Δn of thebirefringence of the liquid crystal device and wavelength dependency ofthe difference Δn of the birefringence of the twisted retardation film10 are compensated, and thus the blackness of the background color isimproved, the displaying color becomes bright and a better negative-typedisplay can be obtained.

The above and other objects, features and advantages of the inventionwill be apparent from the following detailed description which is to beread in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a relation between absorption axes oflower polarizing films and the molecular alignment direction in a liquidcrystal device;

FIG. 2 is also a plan view showing a relation between absorption axes ofupper polarizing films and the molecular alignment direction in atwisted retardation film;

FIG. 3 is a schematic sectional view of the structure of a firstembodiment of a color liquid crystal display according to the presentinvention;

FIG. 4 is a chromaticity diagram explaining changes in color on displayimages when a voltage applied on the liquid crystal device is varied, inthe first embodiment according to the present invention;

FIG. 5 is a plan view showing a relation between absorption axes oflower polarizing films and the molecular alignment direction of a liquidcrystal in a liquid crystal device, obtained when FIG. 7 is viewed fromabove;

FIG. 6 also a plan view showing a relation between absorption axes ofupper polarizing films and the molecular alignment direction in atwisted retardation film;

FIG. 7 is a schematic sectional view of the structure of a secondembodiment of a color liquid crystal display according to the presentinvention;

FIG. 8 is a chromaticity diagram explaining changes in color on displayimages when a voltage applied on the liquid crystal device is varied, inthe second embodiment according to the present invention;

FIG. 9 is a plan view showing a relation between absorption axes oflower polarizing films and the molecular alignment direction of a liquidcrystal in a liquid crystal device, obtained when FIG. 11 is viewed fromabove;

FIG. 10 is also a plan view showing a relation between an absorptionaxis of an upper polarizing film and a phase delay axis of a retardationfilm;

FIG. 11 is a schematic sectional view of the structure of a thirdembodiment of a color liquid crystal display according to the presentinvention;

FIG. 12 is a chromaticity diagram explaining changes in color on displayimages when a voltage applied on the liquid crystal device is varied, inthe third embodiment according to the present invention;

FIG. 13 is a plan view showing a relation between an absorption axis ofan upper polarizing film and a phase delay axis of a retardation film,obtained when FIG. 14 is viewed from above;

FIG. 14 is a schematic sectional view of the structure of a fourthembodiment of a color liquid crystal display according to the presentinvention;

FIG. 15 is a chromaticity diagram explaining changes in color on displayimages when voltage applied on the liquid crystal device is varied, inthe fourth embodiment according to the present invention;

FIG. 16 is a plan view showing a relation between absorption axes oflower polarizing films and the molecular alignment direction of a liquidcrystal in a liquid crystal device, obtained when FIG. 18 is viewed fromabove;

FIG. 17 is also a plan view showing a relation between absorption axesof upper polarizing films and the molecular alignment direction in atwisted retardation film;

FIG. 18 is a schematic sectional view of the structure of a conventionalcolor liquid crystal display using a twisted retardation film;

FIG. 19 is a plan view showing a relation between absorption axes oflower polarizing films and the molecular alignment direction of a liquidcrystal in a liquid crystal device, obtained when FIG. 21 is viewed fromabove;

FIG. 20 is also a plan view showing a relation between an absorptionaxis of an upper polarizing film and a phase delay axis of a retardationfilm; and

FIG. 21 is a schematic sectional view of the structure of a conventionalcolor liquid crystal splay using a retardation film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments to carry out the present invention will beconcretely explained with reference to the drawings.

First Embodiment: FIG. 1 to FIG. 4

A first embodiment of a color liquid crystal display according to thepresent invention will be explained with reference to FIG. 1 to FIG. 4.

FIG. 3 is a schematic sectional view showing the structure of the colorliquid crystal display, FIG. 1 is a plan view showing a relation betweenabsorption axes of lower polarizing film and the molecular alignmentdirection of a liquid crystal in a liquid crystal device, obtained whenFIG. 3 is viewed from the upper polarizing film 9 side, FIG. 2 is also aplan view showing a relation between absorption axes of upper polarizingfilms and the molecular alignment direction in a twisted retardationfilm; and FIG. 4 is a chromaticity diagram.

The structure of the color liquid crystal display is not the same as theconventional color liquid crystal display shown in FIG. 16 to FIG. 18,but since the fundamental constitutions are in common with each other,the portions in FIG. 1 to FIG. 3 corresponding to each portion in FIG.16 to FIG. 18 are given the same reference numeral or symbol, forconvenience of explanation.

In the structure of the color liquid crystal display of the firstembodiment, as shown in FIG. 3, a liquid crystal device 22 is composedholding a nematic liquid crystal 7 in a twisted state between a pair ofsubstrates comprising a first substrate 1 made of a glass plate having athickness of 0.7 mm, there being formed a first electrode 2 and analignment layer 3 thereon, and a second substrate 4 made of a glassplate having a thickness of 0.7 mm, there being formed a secondelectrode 5 and an alignment layer 6 thereon. The first electrode 2 andthe second electrode 5 are transparent electrodes made from ITO (IndiumTin Oxide).

The difference Δn of birefringence of the nematic liquid crystal usedfor the liquid crystal device 22 is set to be 0.2 and the cell gap d,that is a space between the first substrate 1 and the second substrate4, is set to be 8 μm. Accordingly, the Δnd value of the liquid crystaldevice 22 expressed by the product of the difference Δn of birefringenceof the nematic liquid crystal 7 and the cell gap d is 1600 nm.

The alignment layer 3 of the first substrate 1 is processed by a rubbingtreatment parallel to the lower molecular alignment direction 7 a in theliquid crystal shown in FIG. 1, and the alignment layer 6 of the secondsubstrate 4 is processed by a rubbing treatment parallel to the uppermolecular alignment direction 7 b in the liquid crystal.

An optically rotating substance called a chiral material is added to thenematic liquid crystal having a viscosity of 20 cp, and the twist pitchP is adjusted to 16 μm, so that d/P=0.5, to form a liquid crystal devicetwisting 240 degrees counterclockwise.

The twisted retardation film 10 is prepared by the following processes.A cholesteric liquid crystal polymer having a high phase-transitiontemperature is coated on a triacetyl cellose (TAC) film, and afteralignment treatment under high temperature, it is rapidly cooled andsolidified. The film is twisted like the liquid crystal.

The twisted retardation film 10 is disposed between the second substrate4 and the upper polarizing film 9 and the Δnd value of the twistedretardation film, which is expressed by the product of the difference ofbirefringence Δn of the twisted retardation film 10 and the thickness dof the twisted retardation film 10 is set to 1600 nm.

The lower molecular alignment direction 10 a in the twisted retardationfilm 10, shown in FIG. 2, is disposed to be at a position deviating by90 degrees from the upper molecular alignment direction 7 b of theliquid crystal in the liquid crystal device 2, and the upper molecularalignment direction 10 b in the twisted retardation film 10 is designedto twist clockwise by 240 degrees so that it turns reverse to thetwisted angle of the liquid crystal device 22.

The lower polarizing film 8 is disposed outside of the first substrate 1of the liquid crystal device 22, and the upper polarizing film 9 isdisposed outside of the twisted retardation film 10.

The absorption axis 9 a of the upper polarizing film 9, shown in FIG. 2,is disposed to intersect with the upper molecular alignment direction 10b in the twisted retardation film 10 at an angle of 35 degrees, and theabsorption axis 8 a of the lower polarizing film 8 is disposed tointersect with the lower molecular alignment direction 7 a of the liquidcrystal in the liquid crystal device 22 at an angle of 55 degrees. Theintersecting angle between the pair of upper and lower polarizing films8 and 9 is 70 degrees.

A reflecting plate 11 which reflects colored beams that have passedthrough the lower polarizing film 8 is disposed outside of the lowerpolarizing film 8.

In the color liquid crystal display configured as above, when no voltageis applied, linearly polarized light incident from the upper polarizingfilm 9 becomes elliptically polarized light due to the birefringence ofthe twisted retardation film 10, but since the Δnd value of the twistedretardation film 10 is equal to the Δnd value of the liquid crystaldevice 22, it returns to its linearly polarized state in the liquidcrystal device 22. At this moment, since the absorption axis 9 a of theupper polarizing film 9 intersects with the absorption axis 8 a of thelower polarizing film 8 at an angle of 70 degrees, the beam of lightdoes not pass through the lower polarizing film 8, resulting in a blackdisplay.

When voltage is applied between the first electrode 2 and the secondelectrode 5, molecules of the nematic liquid crystal 7 are activated andthe apparent Δnd value of the liquid crystal device 22 is decreased.Consequently, elliptic polarized light generated at the twistedretardation film 10 does not return to a completely linear polarizedstate after passing through the liquid crystal device 22. Therefore, itreaches the lower polarizing film 8 in an elliptical polarization stateand a beam having a specific wavelength passes through the lowerpolarizing film 8 to be viewed as colored light.

The colored beam that passed through the lower polarizing film 8 isreflected by the reflection plate 11 and is again emitted upward throughthe liquid crystal device 22, the twisted retardation film 10 and theupper polarizing film 9 and makes a negative-type color display.

FIG. 4 is a chromaticity diagram in which a curved line 30 shown by asolid line expresses color changes when voltage is gradually increasedfrom the no voltage state in the color liquid crystal display of thefirst embodiment.

With no voltage applied, it is almost monochrome black, but when voltageis applied, it changes to white, then red through yellow, then blue andfinally it becomes green.

By disposing the absorption axis 9 a of the upper polarizing film 9 andthe upper molecular alignment direction 10 b in the twisted retardationfilm 10 to intersect with each other at an angle of 35 degrees, and bydisposing the absorption axis 8 a of the lower polarizing film 8 and thelower molecular alignment direction 7 a of the liquid crystal in theliquid crystal device 22 to intersect with each other at an angle of 55degrees, any difference between the wavelength dependency of thedifference Δn of birefringence of the liquid crystal device 22 and thewavelength dependency of the difference Δn of birefringence of thetwisted retardation film 10 can be compensated and a good bright coloras well as a good black background can be obtained.

Particularly, since with a negative-type display of a black background,incident light from the surroundings of pixels is also blocked, a darkdisplay is obtained. Therefore a brighter displaying color ispreferable.

However, the angle, in the color liquid crystal display of the presentinvention, formed by the absorption axis 9 a of the upper polarizingfilm 9 and the upper molecular alignment direction 10 b in the twistedretardation film 10 is not limited to 35 degrees, and by varying thearrangement in a range of 35 to 40 degrees or 50 to 55 degrees, thedifference between the wavelength dependency of the difference Δn ofbirefringence of the liquid crystal device and the wavelength dependencyof the difference Δn of birefringence of the twisted retardation film 10can be compensated and a good bright color can be obtained.

When the intersecting angle between the upper polarizing film 9 and thelower polarizing film 8 is made smaller than 70 degrees, the displayingcolor gets brighter, but since the black color on the background alsogets thinner, it is preferable to arrange the intersecting angle betweenthe upper polarizing film 9 and the lower polarizing film 8 to be in therange of 60 to 120 degrees.

In addition, the Δnd value of the liquid crystal device and the Δndvalue of the twisted retardation film are adjusted to 1600 nm in thisembodiment, but by adjusting them in a range of 1500 nm to 1800 nm,nearly the same effects can be obtained.

When the Δnd value of the liquid crystal device is made smaller than1500 nm, it is undesirable because the sharpness of the liquid crystaldeteriorates and the high multiplex drive becomes hard to perform, butthis is applicable if the device is a low multiplex drive or activematrix drive.

When the Δnd value of the liquid crystal device and the Δnd value of thetwisted retardation film are set to be larger than 1800 nm, since thecell gap d is required to be thick, it is undesirable because theresponse time of the liquid crystal device becomes slow andcharacteristics of the twisted retardation film 10 are lowered due tovarious difficulties in production.

In the present embodiment, the Δnd value of the liquid crystal deviceand the Δnd value of the twisted retardation film are designed to beequal, but it is possible to make the Δnd value of the liquid crystaldevice larger than the Δnd-value of the twisted retardation film. Whenthe Δnd value of the liquid crystal device is designed to be about 50 nmlarger than the Δnd value of the twisted retardation film, the Δnd valueof the liquid crystal device is reduced under high temperatures so thatthe Δnd value of the liquid crystal device becomes equal with the Δndvalue of the twisted retardation film, which results in the improvementof high-temperature characteristics.

In addition, an STN (super twisted nematic) liquid crystal device havinga 240° twist is used in the present embodiment, but it is possible toobtain a similar effect by using a TN (twisted nematic) liquid crystaldevice having a 90° twist or a STN liquid crystal device having morethan a 180° twist.

Furthermore, since a retardation film made from a liquid crystal polymerin which the twisting state is fixed at room temperature is used as atwisted retardation film in the present embodiment, the Δnd value doesnot change at varied temperatures, but in a temperature-compensatingtype twisted retardation film which undergoes a twist alignment layertreatment so that a portion of the liquid crystal molecules connected toan open chain polymer molecule, the Δnd value varies according to thetemperature change.

When a temperature-compensating type twisted retardation film is used,the change of Δnd value of the twisted retardation film follows thechange of Δnd value of the liquid crystal device caused by thetemperature change. As a result, the color change due to the ambienttemperature is reduced, and the applicable operating temperature rangeis enlarged, resulting in better operation.

Second Embodiment: FIG. 5 to FIG. 8

Next, a second embodiment of the color liquid crystal display accordingto the present invention will be explained with reference to FIG. 5 toFIG. 8.

FIG. 7 is a schematic sectional view showing a structure of the colorliquid crystal display, FIG. 5 is a top plan view showing a relationbetween absorption axes of lower polarizing films and the molecularalignment direction of the liquid crystal in a liquid crystal deviceobtained when the color liquid crystal device shown in FIG. 7 is viewedfrom the top, FIG. 6 is also a top plan view showing a relation betweenabsorption axes of upper polarizing films and the molecular alignmentdirection in a twisted retardation film, and FIG. 8 is a chromaticitydiagram.

In FIG. 5 to FIG. 7, parts corresponding to those in FIG. 1 to FIG. 3are given the same reference numerals and symbols, and the explanationfor these parts is omitted.

The color liquid crystal display of the second embodiment has adifferent configuration from that of the first embodiment with respectto the twisted angle of the twisted retardation film, to upperpolarizing film materials, and to characteristics of the reflectingplate, and is further provided with a back light.

The configuration of the liquid crystal device 22 in the color liquidcrystal display is the same as that of the liquid crystal device 22 ofthe aforementioned first embodiment. The difference Δn of birefringenceof the nematic liquid crystal 7 is 0.2, the cell gap d, that is a spacebetween a first substrate 1 and a second substrate 4, is 8 μm, and theΔnd value of the liquid crystal device 22 is 1600 nm.

An alignment layer 3 of the first substrate 1 is processed by a rubbingtreatment parallel with the lower liquid crystal molecular direction 7a, shown in FIG. 7, and the alignment layer 6 of the second substrate 4is likewise treated parallel with the upper liquid crystal moleculardirection 7 b. An optically rotating substance called a chiral materialis added to a nematic liquid crystal having a viscosity of 20 cp, andthe twist pitch P is adjusted to 16 μm so that d/P=0.5, to form a liquidcrystal device 22 twisting 240 degrees counterclockwise.

To obtain a twist phase different plate 10, a cholesteric liquid crystalpolymer having a high phase transition temperature is coated on a TACfilm, and after an alignment treatment under high temperature, it iscooled and solidified. The twist phase different plate 10 is a filmhaving a twist like a liquid crystal. The twisted retardation film 10 isdisposed outside of the second substrate 4 of the liquid crystal device22 and the Δnd value of the twisted retardation film, which is expressedby the product of the difference Δn of birefringence of the twistedretardation film 10 and the thickness d, is designed to be 1600 nm.

The lower molecular alignment direction 10 a in the twisted retardationfilm 10 shown in FIG. 6 is disposed to take a position deviating fromthe upper molecular alignment direction 7 b of the liquid crystal in theliquid crystal device 22 by 90 degrees. The upper molecular alignmentdirection 10 b in the twisted retardation film 10 shown in FIG. 6 isarranged to be at a twisted angle of 250° clockwise so that it is thereverse direction to the twisted angle of the liquid crystal device.

The lower polarizing film 8 is disposed outside of the first substrate 1of the liquid crystal device 22, and a blue-colored polarizing film 12as an upper polarizing film is disposed outside of the twistedretardation film 10. An absorption axis 12 a of the color polarizingfilm 12, which is shown in FIG. 6, is disposed to be at an angle of 40degrees to the upper molecular direction 10 b in the twisted retardationfilm 10. An absorption axis 8 a of the lower polarizing film 8 shown inFIG. 5 is disposed to be at an angle of 55 degrees to the lowermolecular alignment direction 7 a of the liquid crystal in the liquidcrystal device 22, and the intersecting angle of the lower polarizingfilm 8 and the color polarizing film 12 is 65 degrees.

The upper polarizing film 9 and the lower polarizing film 8 used in thefirst embodiment are made of a drawn film of PVA dyed with iodine, beingput between TAC films, but the color polarizing film 12 is a polarizingfilm dyed with a dichromatic dye instead of iodine. Usually, when twosheets of the color polarizing films are disposed parallel, they show analmost white color having a faint color of the dye. When the colorpolarizing films are disposed intersecting with each other, they show aclear color of the dye.

When two sheets of blue color polarizing films 12 adopted in the presentembodiment are disposed parallel, the device displays in a faint bluishwhite color, but when they are disposed intersecting with each other, itdisplays in navy blue.

As shown in FIG. 7, a transflective reflecting plate 13 is disposedoutside of the lower polarizing film 8, and a back light 14 using anelectro-luminescence (EL) emitting light in white is further disposedoutside of the transflective reflecting plate 13.

Thus, the device consists of a color liquid crystal display serving bothas a reflection-type and a translucent-type. It is usually used as areflection-type color liquid crystal display, but during dark nighttimehours it can be used as a translucent-type color liquid crystal displayby turning on the back light 14.

With no voltage applied, the color liquid crystal display in the secondembodiment shows a navy blue which is the color shown when the colorpolarizing films 12 intersect with each other at right angles, and whenvoltage is applied to the liquid crystal device, it becomes anegative-type color display showing first a pale bluish white, thenreddish violet, blue, and bluish green.

FIG. 8 is the chromaticity diagram and a curved line 31 expressed by asolid line shows the color change caused by the applied voltage on thecolor liquid crystal display of the second embodiment.

In the case of the present embodiment, since some blue light alwaysshines through the color polarizing film 12, saturation of thedisplaying color is interior compared with the case composed with anordinary polarizing film, but by disposing the absorption axis 12 a ofthe color polarizing film 12 and the lower molecular alignment direction7 a of the liquid crystal in the liquid crystal device 22 so as to be atan angle between 35° and 40° or between 50° and 55°, the differencebetween the wavelength dependency of the difference Δn of birefringenceof the liquid crystal device and the wavelength dependency of thedifference Δn of birefringence of the twisted retardation film 10 iscompensated, resulting in a good and bright color.

In addition, by making the absolute value of the twisted angle of thetwisted retardation film 10 to be 10 degrees larger than the absolutevalue of the twisted angle of the liquid crystal device 22,deterioration of the saturation can be reduced and the brightness of thedisplaying color can be improved so that an excellent negative-typecolor display can be provided.

In the present embodiment, the intersecting angle of the lowerpolarizing film 8 with the color polarizing film 12 is made to be 65degrees, but when the intersecting angle is made smaller, the displayingcolor becomes bright. However, since a black color on the backgroundalso becomes pale, a range between 60° and 120° is preferable.

In the present embodiment, the twisted angle of the twisted retardationfilm 10 is made 250°, but when the twisted angle is made larger,although the displaying color becomes bright, the black color on thebackground becomes pale. Therefore, it is preferable to set the absolutevalue of the twisted angle of the retardation film 10 to be larger thanthe absolute value of the twisted angle of the liquid crystal device 22by a range of 5 to 30 degrees.

Furthermore, in the present embodiment, the Δnd value of the liquidcrystal device and the Δnd value of the twisted retardation film 10 are1600 nm, but by setting them in a range of1500 nm to 1800 nm, almostsimilar effects can be obtained. When the Δnd value of the liquidcrystal device is made smaller than 1500 nm, the sharpness of the liquidcrystal is unfavorably lowered and high multiplex drive becomes hard tocarry out, but by making the absolute value of the twisted angle of thetwisted retardation film 10 larger than that of the twisted angle of theliquid crystal device, a color improvement can be similarly obtained,and this is applicable if the device is a low multiplex drive or anactive matrix drive.

Additionally, making the Δnd value of the liquid crystal device and theΔnd value of the twisted retardation film larger than 1800 nm, since thecell gap d is made thicker, is undesirable because the response time ofthe liquid crystal device slows, and moreover the characteristics of thetwisted retardation film 10 deteriorate due to various difficulties inproduction. But a color improvement can be obtained by setting theabsolute value of the twisted angle of the twisted retardation film 10larger than the absolute value of the twisted angle of the liquidcrystal device 22.

In the present embodiment, the blue color polarizing film is used, buteven when a color polarizing film having another color such as red,green, violet or the like, or an ordinary iodine-type polarizing filmhaving a normal color is used, a color improvement can be obtained bysetting the absolute value of the twisted angle of the twistedretardation film larger than the absolute value of the twisted angle ofthe liquid crystal.

Third Embodiment: FIG. 9 to FIG. 12

Next, a third embodiment of a color liquid crystal display according tothe present invention will be explained with reference to FIG. 9 to FIG.12.

FIG. 11 is a schematic sectional view showing a structure of the colorliquid crystal display, FIG. 9 is a top plan view showing a relationbetween an absorption axis of a lower polarizing film and the molecularalignment direction of the liquid crystal in the liquid crystal device,obtained when viewed from the top, and FIG. 10 is a plan view showing arelation between an absorption axis of an upper polarizing film and aphase delay axis of a retardation film. FIG. 12 is a chromaticitydiagram of the color liquid crystal display.

In these drawings, parts corresponding to the parts in FIG. 1 to FIG. 3are given the same numerals and symbols. In the third embodiment, aretardation film 17 is used instead of the twisted retardation film 10used in the first and second embodiments.

The liquid crystal device 23 in the color liquid crystal display has asimilar constitution to that of the liquid crystal device 22 in thefirst embodiment, which is shown in FIG. 3. However, the difference Δnof birefringence of the nematic liquid crystal 7 is 0.21, and the cellgap d, that is a space between the first substrate 1 and the secondsubstrate 4, is 8 μm, so the Δnd value of the liquid crystal expressedby the product of the difference Δn of birefringence of the nematicliquid crystal 7 and the cell gap d is 1680 nm.

The alignment layer 3 of the first substrate 1 is processed with arubbing treatment parallel to the lower molecular alignment direction 7a in the liquid crystal which is shown in FIG. 7. The alignment layer 6of the second substrate 4 is processed with a rubbing treatment parallelto the upper molecular alignment direction 7 b in the liquid crystal. Anoptically rotating substance called a chiral material is added to thenematic liquid crystal having a viscosity of 20 cp, and the twist pitchP is adjusted to 16 μm so that d/P=0.5 is obtained, whereby a liquidcrystal device twisting 240 degrees counterclockwise is obtained.

The retardation film 17 shown in FIG. 11 is a polycarbonate film whichis made by a single axis stretching. Consequently, when the refractiveindex of a phase delay axis 17 a shown in FIG. 10 of the retardationfilm 17 is defined as nx, the refractive index in the Y-axis directionintersecting at right angles with the phase delay axis 17 a is definedto be ny, and the refractive index of the Z-axis direction which is thedirection in thickness is defined to be nz, the resulting relationshipbecomes nx>ny=nz.

The retardation film 17 is disposed outside of the second substrate 4 ofthe liquid crystal device 23, and the retardation value of theretardation film 17 is set to 1800 nm. Accordingly, the retardationvalue of the retardation film 17 is 120 nm larger than the Δnd value ofthe liquid crystal device 23. The phase delay axis 17 a of theretardation film 17 is disposed at a position deviating from the uppermolecular alignment direction 7 b of the liquid crystal in the liquidcrystal device 23 by 85 degrees.

The lower polarizing film 8 shown in FIG. 11 is disposed outside of thefirst substrate 1 of the liquid crystal device 23, and the upperpolarizing film 9 is disposed outside of the retardation film 17. Theabsorption axis 9 a of the upper polarizing film 9 shown in FIG. 10 isdisposed at a position 45° counterclockwise from the phase delay axis 17a of the retardation film 17. The absorption axis 8 a of the lowerpolarizing film 8 shown in FIG. 9 is disposed at a position 35°counterclockwise from the lower molecular alignment direction 7 a of theliquid crystal in the liquid crystal device 23, thus the pair of upperand lower polarizing films 8 and 9 intersect at an angle of 45 degrees.

The reflecting plate 11 which reflects color rays that have passedthrough the lower polarizing film 8 is disposed outside of the lowerpolarizing film 8.

In the color liquid crystal display of the third embodiment of thepresent invention constructed as above, when no voltage is applied,linearly polarized light incident from the upper polarizing film 9becomes elliptically polarized light due to the birefringence of theretardation film 17. Since a difference is set between the retardationvalue of the retardation film 17 and the Δnd value of the liquid crystaldevice 23, and the pair of polarizing films 8 and 9 are disposed at amost suitable angle, the light returns to the linearly polarized statein the liquid crystal device 23. At this time, if the absorption axis 8a of the lower polarizing film 8 and the absorption axis 9 a of theupper polarizing film 9 are disposed in the relation described above,the linearly polarized light does not penetrate through the lowerpolarizing film 8, resulting in a black display.

Next when voltage is applied between a first electrode 2 and a secondelectrode 5 of the liquid crystal device 23, molecules of the nematicliquid crystal 7 are activated and the apparent Δnd value of the liquidcrystal device is decreased. Therefore, the elliptic polarized lightgenerated at the retardation film 17 does not return to a completelylinearly polarized state even after it penetrates through the liquidcrystal device 23. Consequently, it reaches the lower polarizing film 8in a state of elliptical polarization and light having a specificwavelength becomes colored light after penetrating through the lowerpolarizing film 8.

The colored light that penetrated through the lower polarizing film 8 isreflected by the reflecting plate 11 and emits upward again through theliquid crystal device 23, the retardation film 17 and the upperpolarizing film 9, and then performs a negative-type color display.

In the chromaticity diagram shown in FIG. 12, the curved line 32expressed by a solid line shows the color change when the appliedvoltage is gradually increased from the state of no voltage applied inthe color liquid crystal display of the third embodiment. With novoltage applied, it is black with almost no color, but according toincrease of the voltage, it becomes first white, then yellow, red, blueand finally green.

By disposing the absorption axis 8 a of the lower polarizing film 8 andthe lower molecular alignment direction 7 a of the liquid crystal in theliquid crystal device 23 to intersect at an angle of 35 degrees, asshown in FIG. 9, the difference between the wavelength dependency of thedifference Δn of birefringence of the liquid crystal device 23 and thewavelength dependency of the retardation value of the retardation film17 is compensated and a good bright color as well as a good blackbackground color can be obtained.

Especially with a negative-type display having a black background,incident light from surroundings of pixels is also blocked, thusresulting in a dark display. Therefore, a brighter displaying color ispreferable.

When the absorption axis 8 a of the lower polarizing film 8 and thelower molecular alignment direction 7 a of the liquid crystal moleculesin the liquid crystal device 23 are disposed to intersect at an angle ofless than 35 degrees, a bright displaying color can be obtained, but theblack color on the background becomes pale, so that it is thereforepreferable to dispose the absorption axis 8 a of the lower polarizingfilm 8 and the lower molecular alignment direction 7 a of the liquidcrystal in the liquid crystal device 23 to intersect at an angle in arange of 25 to 45 degrees.

In this embodiment, the Δnd value of the liquid crystal device is set to1680 nm, but by setting it in a range of 1500 nm to 1800 nm,substantially similar effects can be obtained. Even in this case, it isnecessary to set the retardation value of the retardation film 17 to belarger than the Δnd value of the liquid crystal device 23 by 50 to 200nm.

When the Δnd value of the liquid crystal device is set to less than 1500nm, it is not preferable because the sharpness of the liquid crystal islowered and high multiplex drive becomes difficult, but this isapplicable if a low multiplex drive or an active matrix drive is used.When the Δnd value of the liquid crystal device is set to more than 1800nn, since the cell gap d is also increased, it is not preferable becausethe response time of the liquid crystal device is delayed andcharacteristics of the retardation film 17 are lowered due to variousdifficulties in production.

When the difference between the retardation value of the retardationfilm 17 and the Δnd value of the liquid crystal device is less than 50nm or larger than 200 nm, it is not preferable because black color onthe background color becomes pale.

In the present embodiment, the absorption axis 9 a of the upperpolarizing film 9 is disposed at an angle of 45° counterclockwise to thephase delay axis 17 a of the retardation film 17, but when theabsorption axis 9 a of the upper polarizing film 9 is disposed at anangle of 45° clockwise to the phase delay axis 17 a of the retardationfilm 17, the display becomes white with no voltage applied, and thedevice becomes a positive display-type color display showning black,blue, green and red with voltage applied.

Additionally, in the present embodiment, an STN (super twisted nematic)liquid crystal device having a 240° twist is used as the liquid crystaldevice, but similar effects can be obtained when a TN (twisted nematic)liquid crystal device having about a 90° twist or an STN liquid crystaldevice having more than a 180° twist is used.

By the way, in the present embodiment, since a retardation film made ofpolycarbonate film is used as the retardation film 17, the retardationvalue does not change even though the ambient temperature changes, butin a temperature compensating-type retardation film in which liquidcrystal molecules are impregnated in the polycarbonate film or a portionof the liquid crystal molecules is connected to open-chain polymermolecules, the retardation value varies according to the temperaturechange.

When the temperature compensating-type retardation film is used, theretardation value change of the retardation film follows the Δnd valuechange of the liquid crystal cell caused by any temperature change. As aresult, the color change due to temperature on the background color isreduced, so the use of the temperature compensating-type retardationfilm is more desirable because the range of applicable operatingtemperatures is increased.

Fourth Embodiment: FIG. 13 to FIG. 15

Next the fourth embodiment of the color liquid crystal display accordingto the present invention will be explained with reference to FIG. 13 toFIG. 15.

FIG. 14 is a schematic sectional view showing the structure of the colorliquid crystal display. FIG. 13 is a top plan view showing the relationbetween the absorption axis of an upper polarizing film and the phasedelay axis of a retardation film, viewed from above. FIG. 15 is achromaticity diagram of the color liquid crystal display.

Incidentally, since the plan view showing the relation between theabsorption axis of the lower polarizing film and the molecular alignmentdirection of the liquid crystal in the liquid crystal device is the sameas FIG. 9, a drawing of the view showing the above relation is omitted.In FIG. 14, portions corresponding to portions in FIG. 7 are given samereference numerals and symbols.

Differences of the color liquid crystal display of the fourth embodimentfrom the aforementioned color liquid crystal display of the thirdembodiment are in the Δnd value of the liquid crystal device 24,materials used for the retardation film 18 and its retardation value,the disposition angle of the upper polarizing film 9 and characteristicsof the reflecting plate 13. Moreover, it is provided with a back light14.

The liquid crystal device 24 in the color liquid crystal display hasalmost a similar configuration as that of the liquid crystal device 22of the first embodiment explained with reference to FIG. 3. However, thedifference Δn of birefringence of the nematic liquid crystal 7 is 0.21and the cell gap d, that is a space between the first substrate 1 andthe second substrate 4, is 7 μm. Therefore the Δnd value of the liquidcrystal device expressed by the product of the difference Δn ofbirefringence of the nematic liquid crystal 7 and the cell gap d is 1470μm.

The alignment layer 3 of the first substrate 1 is processed by a rubbingtreatment parallel with the lower molecular alignment direction 7 a inthe liquid crystal shown in FIG. 9, and the alignment layer 6 of thesecond substrate 4 is processed by a rubbing treatment parallel with theupper molecular alignment direction 7 b in the liquid crystal. Anoptically rotating substance called a chiral material is added to thenematic liquid crystal having a viscosity of 20 cp, the twist pitch P isadjusted to 14 μm so that d/P is made to be 0.5 and thus a liquidcrystal device having a 240° twist counterclockwise is formed.

The retardation film 18 is a biaxially stretched polycarbonate film andwhen the refractive index of the phase delay axis 18 a, shown in FIG.13, of the retardation film 18 is taken as nx, the refractive index inthe y-axis direction intersecting with the phase delay axis 18 a atright angles is taken as ny, and the refractive index in the z-axisdirection, that is a thickness direction, is taken as nz, the relationamong nx, ny and nz is: nx>nz>ny.

In the biaxial retardation film 18, the amount of change in retardationwhen the retardation film 18 is slanted around the y-axis is smallerthan that in the single-axial retardation film 17 used in the thirdembodiment. Therefore, the biaxial retardation film 18 is desirable foruse in a color liquid crystal display since color change caused bychanges of viewing angle are reduced and it has wide viewing anglecharacteristic.

As shown in FIG. 14, the retardation film 18 is disposed outside of thesecond substrate 4 of the liquid crystal device 24 and the retardationvalue is set to 1850 nm. That is, the retardation value of theretardation film 18 is set to be larger than the Δnd value (1470 nm) ofthe liquid crystal device 24 by 380 nm. The phase delay axis 18 a of theretardation film 18 shown in FIG. 13 is disposed at a position deviatingfrom the upper molecular alignment direction 7 b of the liquid crystalin the liquid crystal device 24 by 85 degrees (refer to FIG. 9).

The lower polarizing film 8 is disposed outside of the first substrate 1of the liquid crystal 24, and the upper polarizing film 9 is disposedoutside of the retardation film 18. The absorption axis 9 a of the upperpolarizing film 9 shown in FIG. 13 is disposed 45° clockwise to thephase delay axis 18 a of the retardation film 18, the adsorption axis 8a of the lower polarizing film 8 is disposed 35° counterclockwise (referto FIG. 9) to the lower molecular alignment direction 7 a of the liquidcrystal in the liquid crystal device 24, and the pair of upper and lowerpolarizing films 8 and 9 intersect with each other at an angle of 45degrees.

A transflective reflecting plate 13 is disposed outside of the lowerpolarizing film 8 and a back light 14 using an EL having whiteluminescence is disposed outside of the transflective reflecting plate13.

In the above configuration, the color liquid crystal display of thefourth embodiment serves both as a reflection-type and atranslucent-type color liquid crystal display. That is, during daytimehours, it is used as a reflection-type color liquid crystal display, butduring nighttime hours when ambient illumination is dark, it can be usedas a translucent-type color liquid crystal display, by lighting the backlight 14.

In the color liquid crystal display of the present embodiment, when novoltage is applied, linearly polarized light incident from the upperpolarizing film 9 becomes elliptic polarized light due to thebirefringence of the retardation film 18, but by setting a differencebetween the retardation value of the retardation film 18 and the Δndvalue of the liquid crystal device 24, and by optimizing theintersecting angle of the polarizing films 8 and 9, it returns tolinearly polarized light through the liquid crystal device 24.

At this time, if the relation in disposition between the absorption axis8 a of the lower polarizing film 8 and the absorption axis 9 a of theupper polarizing film 9 is as above, the linearly polarized light doesnot penetrate through the lower polarizing film 8, which results in ablack display.

When voltage is applied on the liquid crystal device 24, it becomes anegative-type color display emitting blue, green and red color accordingto the voltage.

The curved line 33 expressed by a solid line in the chromaticity diagramin FIG. 15 shows the change in color when voltage applied to the liquidcrystal device 24 is gradually increased from no voltage. It is almostblack without color in the no voltage state, but when voltage isapplied, it finally displays red through blue and green colors.

By arranging the absorption axis 8 a of the lower polarizing film 8 andthe lower molecular alignment direction 7 a of the liquid crystal in theliquid crystal device 24 to intersect with each other at an angle of 35degrees, the difference between wavelength dependency of the differenceΔn of birefringence of the liquid crystal device and the wavelengthdependency of the retardation value of the retardation film 12 iscompensated, and a good bright color as well as a good black backgroundcan be obtained.

Particularly, in a negative-type display of a black background, sinceincident light from the surroundings of pixels is blocked, which resultsin a dark display, a rather bright displaying color is preferable.

When the intersecting angle between the absorption axis 8 a of the lowerpolarizing film 8 and the lower molecular alignment direction 7 a in theliquid crystal is made smaller than 35 degrees, the displaying colorgets bright but the black color on the background also gets pale.Therefore it is preferable to arrange the intersecting angle between theabsorption axis 8 a of the lower polarizing film 8 and the lowermolecular alignment direction 7 a of the liquid crystal to be in a rangeof 25 degrees to 45 degrees.

In the present embodiment, the Δnd value of the liquid crystal device 24is set to 1470 nm, but a similar effect can be obtained by setting it ina range of 1300 nm to 1600 mn. Even in such cases, the retardation valueof the retardation film 18 needs to be 300 to 500 nm larger than the Δndvalue of the liquid crystal device 24.

When the Δnd value of the liquid crystal device 24 is set to be smallerthan 1300 nm, it is undesirable because the sharpness deteriorates andhigh multiplex drive becomes hard to perform, but it is applicable if alow multiplex drive or active matrix drive is used.

When the Δnd value of the liquid crystal device 24 is set to be largerthan 1600 nm, it is unfavorable because the final displaying colorchanges from red to white, and the retardation value of the retardationfilm 18 becomes more than 1900 nm, and characteristics of theretardation film 18 deteriorate due to various difficulties inproduction.

When the difference between the retardation value of the retardationfilm 18 and the Δnd value of the liquid crystal device is smaller than300 nm or larger than 500 nm, it is unfavorable because the black coloron the background gets pale.

Additionally, in the present embodiment, the absorption axis 9 a of theupper polarizing film 9 is arranged to have an angle of 45° clockwise tothe phase delay axis 18 a of the retardation film 18, but when theabsorption axis 9 a of the upper polarizing film 9 is arranged to havean angle of 45° counterclockwise to the phase delay axis 18 a of theretardation film 18, a white display occurs with no voltage applied, andit becomes a positive display-type color display displaying greenthrough yellow and blue when voltage is applied.

The type of liquid crystals applicable to this liquid crystal device isthe same as in the cases of each aforementioned embodiment.

The upper polarizing film 9 and the lower polarizing film 8 are made ofdrawn polyvinyl alcohol (PVA) dyed with iodine and are respectively heldbetween sheets of TAC film, but it is possible to change the displayingcolor by adopting a color polarizing film, dyed with a dichromaticcoloring substance instead of iodine, to any one of the upper or lowerpolarizing film or as both of them.

Usually, when two sheets of the color polarizing films are arrangedparallel, the display becomes almost white, though it shows the paledyestuff color used in the polarizing film, but when two sheets of colorpolarizing films are arranged to intersect at right angles, the displayclearly shows the dyestuff color. For instance, when two sheets of bluecolor polarizing films are arranged parallel, a pale bluish white isshown, but when perpendicularly arranged to each other, navy blue isshown.

When the upper polarizing film 9 of the color liquid crystal display ofthe fourth embodiment is replaced by a blue polarizing film, the displayshows navy blue, which is obtainable when color polarizing filmsperpendicularly intersect, with no voltage applied. However when voltageis applied to the liquid crystal device, the display becomes a negativecolor display showing blue, bluish green and finally red.

As described above, according to the present invention, areflection-type color liquid crystal display device producing a brighthigh-saturation negative-type color display having black or a dark colorbackground can be prepared with the simple configuration of a liquidcrystal device, polarizing films and a sheet of retardation films. Inaddition, by practically applying the color liquid crystal display,display for a colorful digital wristwatch, for example, can be obtained.

What is claimed is:
 1. A color liquid crystal display, comprising: aliquid crystal device holding a twist-aligned nematic liquid crystalbetween a pair of substrates made of a first substrate having a firstelectrode and a second substrate having a second electrode; a pair ofpolarizing films disposed holding said liquid crystal devicethereinbetween; and a retardation film, which is made by a single axisstretching, disposed between said liquid crystal device and one of saidpair of polarizing films, wherein an absorption axis of the one of saidpair of polarizing films is disposed at a position 45° counterclockwisefrom a phase delay axis of said retardation film, an intersecting anglebetween an absorption axis of a polarizing film disposed at the oppositeside of said retardation film with respect to said liquid crystal deviceand a lower molecular alignment direction of said liquid crystal in saidliquid crystal device is arranged in a range of 35°±10°, a Δnd value ofsaid liquid crystal device expressed by a product of a difference Δn ofbirefringence of said nematic liquid crystal and a space d between saidpair of substrates is arranged in a range of 1500 nm to 1800 nm; and aretardation value of said retardation film is 50 nm to 200 nm largerthan said Δnd value of said liquid crystal device so that a blackdisplay results when no voltage is applied.
 2. The liquid crystaldisplay according to claim 1, wherein a reflecting plate is providedoutside of the polarizing disposed at the opposite side of saidretardation film with respect to said liquid crystal device.
 3. Theliquid crystal display according to claim 1, wherein at least one ofsaid pair of polarizing films is a color polarizing film made by dyingwith dyestuff.
 4. The liquid crystal display according to claim 1,wherein said retardation film is a temperature-compensating retardationfilm in which a retardation value varies in accordance with temperature.